1. Field of the Invention
The present invention relates generally to optical switches and variable optical attenuators, and, more particularly, to a Switch/Variable Optical Attenuator (“SVOA”) including an integrated Micro-Electro-Mechanical System (“MEMS”) optical switch and MEMS Variable Optical Attenuator (“VOA”).
2. Description of the Related Art
In the past few years, the demand for telecommunications services has increased the bandwidth requirements placed on the major carriers. Accordingly, these major carriers have had to add equipment to handle the increased load. This increases the total board space needed for such equipment, thereby resulting in a need for a reduced product footprint; that is, it would be advantageous to decrease the size of the needed equipment. One method used to decrease equipment size is to develop new-technology products that are inherently smaller and more compact. For example, the industry standard in small-part-count optical switches had been opto-mechanical actuators. These opto-mechanical actuators are being replaced by new devices, based on MEMS technology, that are smaller in size and more reliable.
Integrating several functions into the same package can also effect a size reduction. Unlike electrical components, in which the electrical connections are obtained simply by soldering the components into a circuit board, optical components have fibers that must be connected either by attaching connectors at the ends of the fibers or by fusion spicing the fibers together. Also, room must be left to coil or wrap any extra fiber in such a way that it will not be damaged or kinked. This effectively increases the required board space for each component. Eliminating the fiber and the connection between two components, and integrating the components into a common enclosure, can save board space. A good example of this concept is the technology of planar waveguides. By providing waveguide patterns on a substrate material, various functions can be realized on the same chip.
The advantages of planar waveguide devices do not come without drawbacks. For example, optical switches using planar waveguides tend to be slower and more lossy than MEMS devices. Although the MEMS devices have better performance characteristics, they are generally considered more difficult to integrate. MEMS devices typically depend on free space propagation and mirrors to change the light path. Thus, MEMS devices are limited in the number of functions that can be integrated into a given space. Ideally, it would be desirable to have a device that has the performance characteristics of MEMS devices and the integration factor of planar waveguides.
In the expanding telecommunication field, several combinations of components are becoming standardized. One such combination is the Reconfigurable Optical Add Drop Multiplexer (“ROADM”), illustrated in FIG. 1. ROADMs are being used in almost every node of major optical networks, and will find more uses in other applications, such as inter-office networks.
As illustrated in FIG. 1, a multiplexed optical input signal IN is inputted to an optical demultiplexer 100 where it is demultiplexed into sixteen optical signals, for example. The sixteen optical signals are respectively inputted to sixteen optical switches, indicated at 120, whose respective outputs are provided via respective Variable Optical Attenuators (VOAs) 130 to an optical multiplexer 140. The output of the optical multiplexer 140 is inputted to an optical splitter 150 having one output, OUT, which is the output of the ROADM, and having another output which is inputted to an Optical Channel Monitor (OCM) 160 having Voltage Outputs that may be used for monitoring purposes, these Voltage Outputs reflecting the characteristics of the optical signal inputted to the OCM 160 from the optical splitter 150.
One technique for implementing the ROADM illustrated in FIG. 1 is to use arrayed waveguides for the multiplexer 140 and demultiplexer 100, and to use commercially-available MEMS devices for the switches 120 and the VOAs 130.
The add/drop function of the ROADM is usually performed with a 2×2 switch 220, as illustrated in FIG. 2. Such a 2×2 switch 220 has an Inserted State and a Bypass State. In the Bypass State, the input In is connected to the output Out. In the Inserted State, the ADD input is connected to the OUT output while the input IN is connected to the DROP output. Thus, an incoming signal can either be allowed to pass through, or be dropped out and a new signal inserted in its place. In either case, fluctuations occur in the signal power, and the added signal almost never has the same signal power level as the incoming signal. Accordingly, it is necessary to equalize and level the signal power level. This may be effected by connecting a VOA 130 between the output of the switch 220 and the multiplexer 140 (not shown in FIG. 2). Unfortunately, a connector or fusion splice 210 must be provided between the switch 220 and the VOA 130.
If the switch 220 and VOA 130 of FIG. 2 could be combined, the combination thereof would be simplified by eliminating one package and one connector or splice, and the resulting combination would have a reduced footprint and reduced assembly time, as well as improved reliability. On the manufacturing side, the integration of these two devices would eliminate four fiber end-face preparations and would eliminate one entire device packaging process.